Another Windscreen Wiper problem.

[Ian21401]

Problem: Not every time but becoming more frequent.
Switch on wipers to slow speed and nothing happens. Move switch to fast speed and wipers operate normally. Move switch back to slow speed and wipers continue to operate until switched off. They “park” correctly.
Switch on to slow speed and wipers sometimes operate and sometimes not.
Switch wash/wipe on and washers operate every time but wipers sometimes do not operate.
Intermittent not operating.
I removed the column switch and opened it up. No obvious fault seen. Cleaned up the internal contacts, reassembled and re installed. — No change.
Removed scuttle panel and disconnected wiper motor multiplug. Separate earth lead left attached to it’s earth connection.
Connected jump lead from battery +ve to brown wire pin of multiplug — wiper motor operated immediately at slow speed. Connect jump lead to green wire pin in multiplug — wiper motor operated immediately at fast speed.
Reconnect multiplug and try using column switch — same problem as described at beginning.
Have now removed complete wiper assembly onto workbench but not sure of next step.
Comments courtesy of “brickboard” indicate that there may be a problem with the motor brushes but is it possible to access those brushes and how?
A presentation on YouTube indicates that there is a micro-processer within the motor and how to check the switch wiring resistances but I doubt if my 940 is as sophisticated as that.
Observations and suggestions please.
PS. The motor is an “Electrolux” marked: Volvo. 3518130. 500. W205 Sweden.